The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
The I.E.E.E. standards 802.11a, 802.11b, 802.11g, 802.11n, and 802.16, which are incorporated herein by reference in their entirety, define ways for configuring wireless networks and wireless devices such as client stations and access points. Referring now to FIGS. 1A-1B, a wireless network device may operate in either an ad-hoc mode or an infrastructure mode. In the ad-hoc mode, which is shown in FIG. 1A, each client station 10-1, 10-2, . . . , and 10-N (collectively client stations 10) communicates directly with other client stations.
In the infrastructure mode, which is shown in FIG. 1B, each client station 20-1, 20-2, . . . , and 20-M (collectively client stations 20) communicates with other client stations through an access point (AP) 24. The AP 24 may provide a connection to a network 26, a server 28, and the Internet 30.
Referring now to FIG. 1C, client stations and APs generally include a processor 42, a medium access controller (MAC) device 44, a baseband processor (BBP) 46, and a radio frequency (RF) transceiver 48. The RF transceiver 48 transmits and receives signals through the antenna 49.
Range and throughput (i.e., data rate) of wireless devices may vary depending on environmental conditions. For example, the throughput may decrease as distance and obstructions between a client station and an AP increase. Range and throughput may be increased by using multiple antennas for data transmission and reception.
Some wireless devices use multiple antennas in diversity configurations. In diversity configurations, however, only one antenna is utilized at a time for communication. Consequently, only one set of circuits comprising a RF transceiver, a BBP, etc., is generally used for signal processing. Thus, effective increase in throughput may be marginal.
Alternatively, more than one antenna can be utilized when multiple antennas are used in multiple-input multiple-output (MIMO) configurations. That is, multiple antennas can be utilized simultaneously in MIMO configurations. Specifically, data streams can be transmitted and received through multiple antennas simultaneously. A separate circuit comprising one RF transceiver, one BBP, etc., may be used to process each data stream. That is, an independent set of RF transceivers, BBP, etc., may be used to process data streams associated with each antenna. Thus, antennas may yield higher throughputs in MIMO configurations than in diversity configurations.
MIMO configurations are generally expressed as T×R, where T and R denote number of transmit and receive antennas, respectively. Data streams may be affected by relative locations of transmitting and receiving antennas. By aligning transmitting and receiving antennas relative to one another, a receiver can identify transmissions of each transmitting antenna of a transmitter.
Wireless devices may use different types of antennas. For example, 802.11a-compliant wireless devices use single band antennas of 2.4 GHz bandwidth. 802.11g-compliant wireless devices may use single band antennas of 5 GHz bandwidth. Additionally, 802.11g-compliant wireless devices may use dual band antennas that enable communication in 2.4 GHz and 5 GHz frequency bands since 802.11g-compliant devices are 802.11a-compatible. Similarly, 802.11n-compliant wireless devices may use dual band antennas that enable the wireless devices to communicate in 2.4 GHz and 5 GHz frequency bands.